Agario

The first game from the io games series is Agar.io. You play as a cell, your task is to eat other smaller cells to grow. The more your cell is, the slower it will move.
But you can splitting into several parts to escape or catch up other players. Enjoy and share with your friends!

This game became a sensation in 2016. Now in game appeared a lot of skins + mobile version.
The game developer is Matheus Valadares. You can play this game in full screen mode at OBFOG and watch the video Walkthrough.